Mehdi Mahmoodi

Impact of foaming on the broadband dielectric properties of multi-walled carbon nanotube/polystyrene composites

This study investigated the impact of foaming on the broadband dielectric properties of multi-walled carbon nanotube/polystyrene (MWCNT/PS) nanocomposites. Different carbon nanotube concentrations were prepared by blending of a 20 wt.% MWCNT/PS masterbatch and pure PS using a twin-screw extruder. A chemical blowing agent was used to foam the nanocomposites in a micro injection molding machine. Compression molding was applied to fabricate unfoamed nanocomposites for comparison purposes. Comparing the dielectric properties of unfoamed and foamed nanocomposites showed that foaming increased the percolation threshold, reduced DC and AC conductivities, widened the insulator–conductor transition window, and reduced the dissipation factor of the MWCNT/PS composites. These were attributed to deteriorated conductive network and inferior dispersion and distribution of MWCNTs coming from the presence of foam cells in the nanocomposites. The obtained results propose foaming as a promising technique to improve the dielectric properties of MWCNT/polymer composites.

Experimental Study on Microstructural, Surface Hardness and Flexural Strength of Injection Molded Microcellular Foamed Parts

This paper presents an experimental study on microstructural and mechanical properties of injection molded microcellular foamed parts. The effects of shot size, injection pressure and mold temperature on the relative density, unfoamed skin thickness, cell population density, surface hardness and flexural strength of various regions of the injected parts were investigated. A conventional injection molding machine was modified to produce microcellular acrylonitrile butadiene styrene (ABS) foamed plates. Nitrogen gas was used as the blowing agent. The results showed that surface hardness of microcellular foamed parts are higher and their flexural strength is lower than those of the unfoamed parts. Examining the properties throughout the parts confirmed distinct variations.

Extrusion Foam Coating of Coaxial Cables using Butane as Physical Blowing Agent

This paper presents an experimental study on manufacture and characterization of an insulating foam coating in the coaxial cables where a physical blowing agent (butane) is used. Coaxial cables with foam insulator are widely used in communication industries. The insulating foam plays a key role in the attenuation properties of the coaxial cables. In this research work, an extrusion setup was prepared to produce foam insulated coaxial cable using butane as the physical foaming agent. The effect of die geometry (die gap and die outlet diameter) on foam morphology and loss-attenuation were investigated using a blend of LDPE (90%)-HDPE (10%) as the main material. The results show that an acceptable low loss-attenuation is achievable via using a polyethylene compound and adjusting processing parameters.